HYDRO POWER PLANT
A generating station which utilizes the potential energy of water at a high level for the
generation of electrical energy is known as a “Hydroelectric power station”.
➢ More area is required for reservoir and dam.
➢ It should allow strong foundation with low cost.
➢ There should be no leakage of water in future.
➢ Selected site should have large catchment area, to maintain a certain water level.
➢ Distance of power station site from load centre must not be longer. This is to
minimize the transmission cost.
➢ Construction material shall be available very near.
➢ Submergency area should be minimum.
This is used when p is in KW
Selection of "TURBINE"
The purpose of the casing is to provide an even distribution of water around the circumference of the turbine runner. The cross section area of the casing is gradually decreased to keep the velocity of water constant through out it’s path.
➢ Speed ring or stay ring :
The purpose of ring is to direct the water from the spiral casing to the guide vanes
or wicket gates.
➢ Guide vanes or wicket gates :
The function is to regulate the quantity of water supplied to the runner and to direct
water on the runner at an angle appropriate to design.
generation of electrical energy is known as a “Hydroelectric power station”.
1) selection of site:
➢ Sufficient quantity of water at a reasonable head should be available.➢ More area is required for reservoir and dam.
➢ It should allow strong foundation with low cost.
➢ There should be no leakage of water in future.
➢ Selected site should have large catchment area, to maintain a certain water level.
➢ Distance of power station site from load centre must not be longer. This is to
minimize the transmission cost.
➢ Construction material shall be available very near.
➢ Submergency area should be minimum.
2) Schematic arrangement of Hydroelectric power station.
(1) Hydraulic structure :
(a) water reservoir :
It’s purpose is to store water which may be utilized to run the prime mover to produce electrical power.
(b) Dam :
The function of dam is to provide a head of water to be utilized in the water turbine.
(c) Trash rack :
Trash rack of steel bars is placed across the intake at the begging of water conductor system. To prevent entering of debris which might damage the wicket gates and turbine runners.
(d) fore bay :
The fore bay server as a regulatory reservoir storing water temporality when load an the plant is reduced and to supply extra water required when load increases suddenly.
penstock.
It is to provide better regulation of flow of water when the load on system fluctuates.
(f) Pen stock :
It supplies water to the turbine from surged tank as force bay.
It is made of steel or concrete and designed as a pressure flow pipe.
It is supported on anchor blocks.
(g) Spill way :
Spill ways servers to discharge excess water from the reservoir.
(i) Classification based on direction of flow.
(a) Axial flow turbine:
It is used where flow is parallel to the axis of rotation of the turbine.( propeller or
kalpan)
(b) Tangential flow turbine
Flow is tangential to the path of rotation(pelton).
(c) Mixed flow turbine
Water enters the runner at the outer periphery in the radial direction and leaves it at
the centre in axial direction.
(ii) Classification based on action of water.
(a) Impulse turbine:
In this turbine, all the available energy of water is converted into kinetic energy of
velocity head by passing through a nozzle provided at the end of pen stock.(pelton
wheel turbine)
(b) Reaction turbine
In this turbine , available energy of water remains mostly as pressure energy. As the
water flows through the runner, the pressure energy gradually decreases. Therefore, the
runner must be enclosed in an air tight casing.(francis, propeller, kaplan turbines)
Where, N=actual speed in r.p.m.
H=Head in meters
(e) Surge tank :
It is a large cylindrical tank provided near the down stream and of the long penstock.
It is to provide better regulation of flow of water when the load on system fluctuates.
(f) Pen stock :
It supplies water to the turbine from surged tank as force bay.
It is made of steel or concrete and designed as a pressure flow pipe.
It is supported on anchor blocks.
(g) Spill way :
Spill ways servers to discharge excess water from the reservoir.
(2) Water turbines :
Water turbines are used to convert the energy of falling water into mechanical energy.(i) Classification based on direction of flow.
(a) Axial flow turbine:
It is used where flow is parallel to the axis of rotation of the turbine.( propeller or
kalpan)
(b) Tangential flow turbine
Flow is tangential to the path of rotation(pelton).
(c) Mixed flow turbine
Water enters the runner at the outer periphery in the radial direction and leaves it at
the centre in axial direction.
(ii) Classification based on action of water.
(a) Impulse turbine:
In this turbine, all the available energy of water is converted into kinetic energy of
velocity head by passing through a nozzle provided at the end of pen stock.(pelton
wheel turbine)
(b) Reaction turbine
In this turbine , available energy of water remains mostly as pressure energy. As the
water flows through the runner, the pressure energy gradually decreases. Therefore, the
runner must be enclosed in an air tight casing.(francis, propeller, kaplan turbines)
Specific Speed of Turbines :
It is defined as the hypothetical speed of the turbine at which it produce 1 H.P. of the power under heat of L meter. It is an important parameter in design of turbines.
P=Power in h.p. (735.5 watts)
This is used when p is in KW
Selection of "TURBINE"
Francis turbine
Parts of francis turbine :
➢ Spiral casing :The purpose of the casing is to provide an even distribution of water around the circumference of the turbine runner. The cross section area of the casing is gradually decreased to keep the velocity of water constant through out it’s path.
➢ Speed ring or stay ring :
The purpose of ring is to direct the water from the spiral casing to the guide vanes
or wicket gates.
➢ Guide vanes or wicket gates :
The function is to regulate the quantity of water supplied to the runner and to direct
water on the runner at an angle appropriate to design.
➢ Runner :
It consist of a series of curved vanes around the circumference to change the direction of flow of water when it passes through the runner. The runner is keyed to a shaft.
➢ Draft tube :
It is a pipe or passage of gradually increasing cross-sectional area which connects the runner exit to the tail race. The lower end must be submerged below the level of water in the tail race.
➢ Governing of turbines :
The operation of regulation of speed of turbine runner is known as “governing of
turbines”. It is done automatically by means of “governer”.
➢ Runway speed :
This is the maximum speed at which a turbine wheel would run under the worst
conditions of operation with all gates open so as to allow the possible water inflow under max. head.
(3) Alternator :
Hydroelectric generators are low speed m/c of the salient pole type, having a large
no. of poles, a large diameter and a short rotor. The speed of the hydroelectric generator depends upon the turbine driving it, which is in turn depends on the specific speed of the particular type of turbine generally generation is 3.3 or 11 kv at 50 Hz.
(4) Classification of H.P.P. :
➢ Classification based on load characteristics.
1. Base load plants:
▪ The plant operates on the large amount of the load curve.
▪ Generally it’s capacity is large and high load factor.
▪ Runs continuously through out the year.
2. Peak load plants :
▪ It operates only during period of peak load. Hence short period of total operating
time.
▪ Pumped storage plants are usually designed as peak load plants.
➢ On the basis of hydraulic or storage consideration :
1. Run-off the river plant:
The plant uses the water as it comes in the river. This type of power plants has no
control over the river flows. It does not store the water.
During rainy season high water flow is available and if the power plant is not able
to use this large flow of water some quantity of water is allowed to flow over dam
spillways as waste.
During dry season, the power produced by such plants will be such will be low, due
to low flow rates. The utility of this plants are very less due to uncertainty of power
supply.
2. Run-off plants with pondage :
The pond permits to store water during off peak hours and uses during peak hours
of the same day.
3. Storage plants :
A dam is constructed across the river to create a large reservoir for storing water
during rainy season and the water is released whenever required.
The advantages of this plant is that the power generated by the plant during dry
season will not be affected.
4. Pumped storage plant :
Pumped storage plant is combination with hydroelectric power plant is used for
supplying the sudden peak load of short duration.
During the off-peak period , water is pumped back to the head water pool from the
tail water pool during the peak demand the water is drawn from the head water pool to generate power to meet the peak demand.
It uses "reversible turbine”.
➢ Water head:
The difference of water level is called the “water head”.
➢ Gross head:
The total head difference between the water levels in head race and tail race is
called as “gross head or total head”.
➢ Net head or effective head:
Gross head –head loss in the conveyor system from head race to the entrance of
turbine due to friction.
➢ Rated head :
Head utilized in doing work on the turbine is called the rated head.
Rated head = Net head – loss in guide passage and entrance of turbine.
➢ Power Output :
Where, W=Specific weight of water=981 kg/m.sq.
H=Net head of water in meter on the turbine.
Q=Quantity of water in m.cube/sec.
n=Overall efficiency of the system.
Where, W=1000kg/m.cube
➢ Hydrograph :
It is a graph between discharge and time in chronological order.
➢ Mass curve :
It is a plot of cumulative volume of water that can be stored from stream flow
versus time.
➢ Flow duration curve :
It is a graph between the discharge and the percentage of time the discharge
equalled or exceeded.
➢ Power duration curve:
The power duration curve is similar to flow duration curve replacing flow power in
kw or h.p.
It consist of a series of curved vanes around the circumference to change the direction of flow of water when it passes through the runner. The runner is keyed to a shaft.
➢ Draft tube :
It is a pipe or passage of gradually increasing cross-sectional area which connects the runner exit to the tail race. The lower end must be submerged below the level of water in the tail race.
➢ Governing of turbines :
The operation of regulation of speed of turbine runner is known as “governing of
turbines”. It is done automatically by means of “governer”.
➢ Runway speed :
This is the maximum speed at which a turbine wheel would run under the worst
conditions of operation with all gates open so as to allow the possible water inflow under max. head.
(3) Alternator :
Hydroelectric generators are low speed m/c of the salient pole type, having a large
no. of poles, a large diameter and a short rotor. The speed of the hydroelectric generator depends upon the turbine driving it, which is in turn depends on the specific speed of the particular type of turbine generally generation is 3.3 or 11 kv at 50 Hz.
(4) Classification of H.P.P. :
➢ Classification based on load characteristics.
1. Base load plants:
▪ The plant operates on the large amount of the load curve.
▪ Generally it’s capacity is large and high load factor.
▪ Runs continuously through out the year.
2. Peak load plants :
▪ It operates only during period of peak load. Hence short period of total operating
time.
▪ Pumped storage plants are usually designed as peak load plants.
➢ On the basis of hydraulic or storage consideration :
1. Run-off the river plant:
The plant uses the water as it comes in the river. This type of power plants has no
control over the river flows. It does not store the water.
During rainy season high water flow is available and if the power plant is not able
to use this large flow of water some quantity of water is allowed to flow over dam
spillways as waste.
During dry season, the power produced by such plants will be such will be low, due
to low flow rates. The utility of this plants are very less due to uncertainty of power
supply.
2. Run-off plants with pondage :
The pond permits to store water during off peak hours and uses during peak hours
of the same day.
3. Storage plants :
A dam is constructed across the river to create a large reservoir for storing water
during rainy season and the water is released whenever required.
The advantages of this plant is that the power generated by the plant during dry
season will not be affected.
4. Pumped storage plant :
Pumped storage plant is combination with hydroelectric power plant is used for
supplying the sudden peak load of short duration.
During the off-peak period , water is pumped back to the head water pool from the
tail water pool during the peak demand the water is drawn from the head water pool to generate power to meet the peak demand.
It uses "reversible turbine”.
➢ Classification based on head
There are no rules to classify according to head. But, generally taken as- Low head (<30 m)
- Medium head (30-250 m)
- High head (>250 m)
➢ Water head:
The difference of water level is called the “water head”.
➢ Gross head:
The total head difference between the water levels in head race and tail race is
called as “gross head or total head”.
➢ Net head or effective head:
Gross head –head loss in the conveyor system from head race to the entrance of
turbine due to friction.
➢ Rated head :
Head utilized in doing work on the turbine is called the rated head.
Rated head = Net head – loss in guide passage and entrance of turbine.
➢ Power Output :
H=Net head of water in meter on the turbine.
Q=Quantity of water in m.cube/sec.
n=Overall efficiency of the system.
➢ Hydrograph :
It is a graph between discharge and time in chronological order.
➢ Mass curve :
It is a plot of cumulative volume of water that can be stored from stream flow
versus time.
➢ Flow duration curve :
It is a graph between the discharge and the percentage of time the discharge
equalled or exceeded.
➢ Power duration curve:
The power duration curve is similar to flow duration curve replacing flow power in
kw or h.p.
Advantages of Hydroelectric power plants
➢ Zero fuel cost.
➢ Low maintenance.
➢ High power efficiency.
➢ Plant is free from pollution.
➢ Can be used as multi-purpose projects.
➢ Cost per unit is less.
➢ Suitable for variable heads and to act as a peak load plant.
Disadvantages of Hydroelectric power plants
➢ Requirement of area is more.
➢ High initial cost.
➢ Located in remote area and requires more transmission cost.
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